A design method for first-order pulse-width modulated system†

Abstract

Puke-width modulated control systems are very attractive for the practising control engineer due to their low cost, and ruggedness of design. Unfortunately these interesting features are impaired by the mathematical difficulties associated with the design of these systems, as they are known to be highly non-linear. In most cases the practising control engineer must resort to simulation or bench design in order to achieve desired objectives both in transient and steady-state specifications. This paper presents a method to overcome these problems and shows how the design of pulse-width modulated systems may be achieved using standard Z transform synthesis techniques. The method's main characteristic is to use a special non-linear modulator whose function is to linearize the relationship between the modulator's control signal and the output of the controlled process; this result is obtained by the addition of a model of the process to the modulator The method may be used for any modulated functions but is basically restricted to the case in which the controlled process may be modelled by a dominant time-constant and a delay; actually this is not a serious drawback as most industrial processes may be described by such a model Different types of modulators are analysed and a design example is presented to illustrate the simplicity of the method